In recent years, an increasing prevalence of obesity in inflammatory bowel disease (IBD) has been observed. Obesity, moreover, has been directly correlated with a more severe clinical course and loss of response to treatment.

To assess the prevalence and associated factors of obesity in IBD.

We collected data about IBD disease pattern and activity, drugs and laboratory investigations in our center. Anthropometric measures were retrieved and obesity defined as a body mass index (BMI) > 30. Then, we compared characteristics of obese vs non obese patients, and Chi-squared test and Student’s t test were used for discrete and continuous variables, respectively, at univariate analysis. For multivariate analysis, we used binomial logistic regression and estimated odd ratios (OR) and 95% confidence intervals (CI) to ascertain factors associated with obesity.

We enrolled 807 patients with IBD, either ulcerative colitis (UC) or Crohn’s disease (CD). Four hundred seventy-four patients were male (58.7%); the average age was 46.2 ± 13.2 years; 438 (54.2%) patients had CD and 369 (45.8%) UC. We enrolled 378 controls, who were comparable to IBD group for age, sex, BMI, obesity, diabetes and abdominal circumference, while more smokers and more subjects with hypertension were observed among controls. The prevalence of obesity was 6.9% in IBD and 7.9% in controls (not statistically different; P = 0.38). In the comparison of obese IBD patients and obese controls, we did not find any difference regarding diabetes and hypertension prevalence, nor in sex or smoking habits. Obese IBD patients were younger than obese controls (51.2  ± 14.9 years vs 60.7 ± 12.1 years, P = 0.03). At univariate analysis, obese IBD were older than normal weight ones (51.2 ± 14.9 vs 44.5 ± 15.8, P = 0.002). IBD onset age was earlier in obese population (44.8 ± 13.6 vs 35.6 ± 15.6, P = 0.004). We did not detect any difference in disease extension. Obese subjects had consumed more frequently long course of systemic steroids (66.6% vs 12.5%, P = 0.02) as well as antibiotics such as metronidazole or ciprofloxacin (71.4% vs 54.7%, P = 0.05). No difference about other drugs (biologics, mesalazine or thiopurines) was observed. Disease activity was similar between obese and non obese subjects both for UC and CD. Obese IBD patients suffered more frequently from arterial hypertension, type 2 diabetes, non-alcoholic fatty liver disease. Regarding laboratory investigations, obese IBD patients had higher levels of triglyceridemia, fasting blood glucose, gamma-glutamyl-transpeptidase. On multivariate analysis, however, the only factor that appeared to be independently linked to obesity in IBD was the high abdominal circumference (OR = 16.3, 95%CI: 1.03-250, P = 0.04).

Obese IBD patients seem to have features similar to general obese population, and there is no disease-specific factor (disease activity, extension or therapy) that may foster obesity in IBD.

Obesity is a growing problem in developed countries, since it is going to become the leading cause for mortality due to cardiovascular events[1]. In Italy, it is estimated that about the 18% of population is suffering from obesity[2]. The World Health Organization (WHO) defines obesity by a value of body mass index (BMI) above 30 kg/m², but obesity underlies as well an excessive visceral fat distribution, with several alterations at hormonal, inflammatory and endothelial level[3]. Inflammatory bowel disease (IBD) is a group of chronic inflammatory autoimmune disorders of gastrointestinal tract, mainly represented by Crohn’s disease (CD) and ulcerative colitis (UC). The problem of obesity is spreading in the context of IBD, since, in the past, it has been rarely recognized for the frequent association between IBD and malnutrition. However, nowadays, novel and more effective drugs are able to stop the progression of the disease, thus preventing malnutrition[4]. Indeed, a study performed in 2002 found a prevalence of obesity in CD of about 3%[5]; one decade later, however, in another study a prevalence of 31.5% was recorded[6]. Co-occurrence of obesity and IBD is not just a casual phenomenon and it has been emphasized that obesity may lead to a higher risk of perianal complications, higher hospitalization rates and greater risk of disease flares[5]. Moreover, obese patients with IBD on azathioprine were more likely to need courses of systemic corticosteroids and had higher recurrence rates after stopping the drug[7]. Furthermore, it has been estimated that an increase of one unit of BMI may increase the risk of therapeutic failure of 4%[8] and, in particular, a high BMI was an independent predictor of adalimumab therapy failure[9]. Considering that IBD per se could increase the risk of endothelial dysfunction and cardiovascular risk[10,11], the association between obesity and IBD may represent a very important issue.

Therefore, we aimed, in a case-control study, to investigate the prevalence of obesity in IBD patients and detect possible factors associated to this condition.

The prevalence of obesity in IBD, a hot topic at the moment, has been investigated in several studies, showing highly variable values ranging from 5% to 30%[5,6]. A Scottish study based on a population of 489 IBD patients showed that 18% of patients had the features of obesity (compared to 23% of the general population); obese patients with CD were 18%, while obese patients with UC were 17.5%[14]. In the present study, we found a similar prevalence between controls and IBD which seems to confirm data from literature. The obesity rate in our cohort (6.9%) was only slightly lower than the 10.8% in the general population reported according to the European Eurostat survey[15]. Our results, additionally, underline that obesity in IBD patients has some peculiar features in comparison with obese controls. In detail, obese IBD subjects are younger than control counterpart, and this could be explained by the fact that, during the history of the disease, some factors such as steroid consumption could have favored weight gain. However, only at univariate analysis, steroid use was a predictor of obesity in IBD even if we were able to evaluate simply the exposure, and not its amount, and this could be considered as a limitation in our study. Additionally, the number of relapses occurred during the clinical history of patients was not collected from medical records, and this could be another limitation. Another feature of obese IBD patients is that they tend to have less frequently a large abdominal circumference than obese controls (Figure 2G), thus suggesting the possibility that fat distribution could be also localized in areas different than waist, such as hip or limbs. Indeed, some studies evidenced that in IBD the ratio between visceral and subcutaneous fat is altered[16] compared to healthy population, and this may explain our finding. Unfortunately, we did not take other anthropometric measurements, therefore we were unable to confirm this hypothesis.

Furthermore, we did not find any correlation between disease activity and BMI. This could be in disagreement with some literature data, showing that visceral fat[17,18] and high BMI[19] are associated with a dismal prognosis. However, our study was cross-sectional, therefore we could not evaluate the evolution of the disease during a follow up period. This could be acknowledged as another limitation. Nevertheless, some other studies did not find a strong association between BMI and disease activity and prognosis[20-23], and this underlines how this topic is still debated and with conflicting evidences.

Another important finding was that only the abdominal circumference was independently associated with obesity in IBD. We are aware that this could be an obvious result, but if we consider that it was not very common in our cohort (less than 50%), it is noteworthy to be underlined. Systemic steroids were associated with obesity only at univariate analysis, and this is an easily comprehensible link that has been already elucidated in literature[24]. Another interesting result was the most extensive use of antibiotics in obese IBD subjects. It is presumable that they could promote a dysbiosis, which in turn might facilitate the development of obesity, as already suggested by many clinical and basic science studies[25]. Finally, the high risk of diabetes, hypertension and liver steatosis is a well know phenomenon that seems to be related to obesity rather than to IBD itself[26].

In conclusion, our study may lay the foundation for some additional speculations. Since epidemiologically IBD are increasing in developed countries, the pathogenetic role and influence on the outcome of disease played by the diet should not be underestimated and must be further investigated. In this regard, it has been already demonstrated that IBD patients, even in remission phase, tend to have a high lipid and low fiber intake[27]. Furthermore, It may be useful to plan new clinical studies aimed at evaluating clinical, laboratory and endoscopic parameters at the baseline and following BMI changes induced by dietary regimens, since this topic is still very poorly investigated.